Preparation of metal hydrides



Dec. 8, 19331. F. H. DRIGGS PREPARATION OF METAL HYDRIDES Filed Nov` 25,1929 l .200 300 TEMP. "C

0 0 M 0 0 o 0 0 7 w 5 4 3 w m 5 Patented Dec. 8, 1l

SATES FRANK H. DRIGGS, OF BLOOMFIELD, JERSEY, ASSIGNOR TO WESTINGHOUSELAMP COMPANY; A CORPORATION OF PENNSYLVANIA.

PREPARATION OF METAL H'YDBIDES Application led November 25, 1929. SerialNo. 409,443.'

,409,442 filed November 25, 1929, entitled Preparation metal hydrides,which is assigned to the same assignee as the present invention I havedisclosed a method of preparing metal hydrides from metal powders,particularly the rare refractory metal pow ders, which form compoundswith atmospheric gases which -are irreducible by hydro- The methoddisclosed therein sets forth a degasiication of the metal powder steppreliminary to the formation of the hydride compound. The degasiiicationof the metal powder by the method disclosed therein is a slow andtedious process and on any commercial scale materially increases thecosts of manufacture. Moreover with the more highly reactive metals,such as uranium and thorium, it. is exceedingly dicult to perform thcstep without deleterious contamination of the metal with the residualgases in the evacuated system.

It is one of the objects of this invention to improve. the method ofpreparing metal hydrides.

It is another object to provide a method of preparing metalhydridesdirectly from presi ntered. substantially pure gas free coherent metalbodies.

It is another object of this invention to provide a. method. of formingmetal hydrides from sintered coherent masses of rare refractorv metals.

4In accordance with the objects of the present invention I have foundthat a `solid mass of coherent metal may be entirely converted -of thepresent invention I over to hydride by forming upon the metal surfacemetal hydride compounds, effecting thermal decomposition of thesecompounds with consequent corrosion of the metal surface, again formingsurface hydride compounds and repeating the thermal decomposit-ion andforming of fresh hydride until the entire coherent metal body has beenconverted over tothe hydride. In the practice substantially follow thepractice of my copending application above identified, in that the metalsurface is first exposed to the action of hydrogen at an elevatedtemperature, the hydrogen pressure being maintained above theequilibrium pressure of the metal hydride compound `at the temperatureemployed, promoting thereby the formation of surface metal hydridecompounds.

The temperature of the metal body is then materially increased, or thehydrogen pressure is reduced below the ,equilibrium pressure, or bothfactors are varied soas to effect a decomposition of the metal hydrideto metal powder, which crumbles `or falls away from the coherent metalmass thereby exposing fresh metal surfaces of the mass. The freshlyexposed. metal surface is again subjected to the. action of thehydrogen, preferably at a lower combining temperature, the hydrogenpressures being meanwhile adjusted to be in excess to the equilibriumpressure. of the metal hydride compound at that temperature. Thisoperation is repeated as many times as is requiredto effect the entirecon- Version of the coherent metal mass to metal hydride compounds, allas will be more fully hereinafter disclosed.

j Before further disclosing the nature of this invention referenceshould be had to the accompanying drawings wherein,l

Fig. 1 is a schematic diagram of the apparatus employed in the practiceof the present invention, and

Fig. 2 is a graphical representation of the apparatus (not shown) such`as mercurydiffusion pumps, molecular pumps, oil immersion pumps and thelike apparatus capable of giving a high vacuo in container 2 of theorder of 1.0 micron pressure which is equivalent to a pressure of about.001 m. m.

mercury. Means are provided for prevent-- ing the dispersion of oil,mercury or other deleterious vapors from the mechanical exhaust means tothe container 2, such as trap 5, which may be surrounded by a suitableliquid air container, not shown.

Means comprising a stop cock 6 are also provided for closing ofi' theexhaust appa-v ratus and means comprising a stop cock 7 are provided forintroducing hydrogen gas under pressure to the evacuated container froma reservoir, not shown but indicated. Pressure reading means 8 areprovided for determining the pressure of the hydrogen in the system 3which in the present illustration comprises a long glass tube extension9 of the system 3 dipping into a container 10 which is open to theatmosphere and filled with mercury 11, and means comprising stop cock 12are provided for shutting off this lpressure reading means 8 when sodesired.

Heating means comprising a wire wound resistance furnace or oven 13provided with temperature measuring means 14 are provided to heat themetal body 1 to the desired temperature. A two piece top 15 forenclosing the container 2 within the furnace 13 is also provided.

In accordance with the present invention the coherent body of metal 1may be comprised of one of the rare refractory metals uranium, thorium,zirconium, titanium, hafnium and the like, and preferably has beenprepared from substantially pure metal powder prepared in accordancewith the invention set forth in U. S. Patent 1,704,257 issued March 5,1929 to J. W. Marden et al., or by any one of the electrolytic methodsset forth in my eopending applications Serial No. 275,264, filed May 4,1928, Serial No. 277,096 led May 11, 192s, serial N0. 309.682 filedOctober 1, 1928, Serial No. 316,624 filed November 1, 1928, or SerialNo. 351,451 filed March 30, 1929 which patent and copendingapplications' are all assigned to the same assignee as the presentinvention.

The substantially pure rare refractory metal powder is then compactedand heattreated to a coherent body in a continuously maintained highvacuo, in accordance with the process set forth in copending applicationSerial No. 717,940 led June 5, 1924 by J. W. Marden, et al. whichapplication is also assigned to the same assignee as the presentinvention.

Briefly the sintering process contemplates the heat-treatin of themetal, body in vacuo in two stages; rst, at a relatively low temperatureto effect the removal of adsorbed and absorbed gases from the compactedmetal powder at a temperature substantially below the combiningtemperature of the metal powder for the gases, and secondly at a highertemperature approximating the fusionpoint of the compacted metal powderto effect the coalescing and sintering of the degasified metal powderinto a coherent metal body, the said two heat treatments being appliedthereto in consecutive order without intervening exposure of the meal todeleterious gaseous absorption.

By this method of sintering the metal powders of the more highlyreactive rare refractory metals into a coherent metal body a metal massis obtained which is substantially free of deleterious impurities ofoxides, nitrides, hydrides and the like compounds.

The forming of metal hydrides from a coherent metal bodT of the rarerefractory metals uranium, t orium, zirconium, hafnium and the like, ishighly desirable in that the amount of deleterious impurities introducedinto the resulting hydride is relatively extremely low. This is believedto be due to the fact that the two stage vacuum heat treating step tocoherent form, as by the above identified copending application SerialNo. 717,940, more completely eliminates the deleterious adsorbed andabsorbed gases of the metal powder prior to sintering than is obtainedby the practice of the relatively lower degasification heating stage ofthe above identified copending application filed herewith.

Another advantage is in the relatively short period of time required toeffect degaslfication or removal of the surface gases of a coherentmetal body prior to the preparation of the m'etal hybride. f

In the practice of the present invention and as a specific `embodimentthereof I will disclose the method I employ in the forming of uraniumhydride from a coherent body of uranium.

The uranium metal body 1 prepared and sintered as above disclosed inaccordance with the inventions of the above identified portion 16thereof in the manner shown, and

.the container 2 connected to the evacuating system 3 by means of thetapered stopper 4, and the entire system evacuated with stop cocks 7 and12 closed. When a relatively high vacuo has been obtained by mechanicalexhaust means, trap is surrounded by a suitable. liquid air container topreventI the back dispersion of deleterious vapors or gases. Container 2and metal body 1 is then thoroughly baked and freed of surface gases bybringing the' temperature of the enclosing furnace or oven up to'temperatures just below the softening temperature of the container 2.The uranium metal body may also be heated to incandescence if desired byhigh frequency' induction means.

When a pressure of about 1.0 micron.. (.001 m. 1n. mercury) has beenobtained in .the system the evacuating system is closed by means of stopcock 6, the uranium metal button allowed to cool to about roomtemperature and the system then filled with pure dry hydrogen from thehydrogen reservoir (not shown but indicated)` by opening stop cock 7,and the pressure of the gas adjusted to about 150 m. m. as determined bymeans of the pressure reading device 8.

The temperature of the uranium metal body is then brought up to about225 C. at which temperature, reaction of the uranium with the hydrogenatmosphere takes place and proceeds as long as the hydrogen pressureexceeds a pressure of about 3 m. m. of mercury, as is shown in Fig. 2and more fully set forth in copending application filed herewith. Theabsorption or reaction of the uranium with the hydrogen proceeds rapidlyuntil the surface is completely coated and then the rate of combinationslows up and eventually the further formation of metal hydride issubstantially prevented.-

By the next step of my invention I raise the temperature of the metalbody to about 350 to 400o C. at which temperature the equilibriumpressure for hydrogen and uranium hydride is between Labout 80 and 320m. m. mercury and effect thereby a decomposition or dissociation of theuranium hydride compound formed in the first step, the metal powderproduct of the decomposition falls away from the surface of the coherentmass and collects in the bottom of the container 2in the manner shown. Ithen reduce the temperature of the container 2 to about 225 (l again,form more hydride upon the uranium metal body and repeat thedecomposition of the hydride by again increasing the temperature to 350to 400 C. This is repeated as many times as is required to entirelyconvert the uranium body over to the hydride compound which iseventually collected as a loose powder in the bottom of the container 2.

From the weight of the uranium metal body 1 the approximate amount ofhydrogen required to effect entire conversion may be readily calculated,and the capacity of the system 3 adjusted by means of suitable res- 05ervoirs 17 to hold the same, and suitable pre- 'body it is apparent thatthere may be many cautions must be taken so that the system will safelcarry the higher pressures of gases re uired by this method.

n alternative method would be to evacuate thc hydrogen from the systemwhen reaction between the uranium metal surface and the hydrogen hasceased, or toreduce the pressure below the equilibrium pressure at theinitial combining temperature of 225 C. effecting thereby thedissociation of the uranium hydride compound, or a still highertemperature in combination With the reduced pressures may be employed toobtain substantially the same effect as is obtained in the firstillustration of the practice of my invention.

While I have disclosed herein the specific method I employ in producinguranium hydride from a coherent uranium metal modifications made thereinin both the process and apparatus Without substantially departing fromthe nature of the invention, and that the invention is adaptable to beemployed in the manufacture of other metal hydrides'than uranium,.andthat such modications, departures and applications thereof areanticipated as may fall within the kscope of the following claims.

What is claimed is:

1. The method of converting coherent metal bodies into metal hydridecompounds which comprises converting the surface of the metal. body tohydride, effecting thermal decomposition of said hydride, and repeatingthe process until entire conversion of the metal body has been effected.

2. The method of converting coherent meta-l bodies into metal hydridecompounds which comprises repeatedly heating the metal body in hydrogento a temperature at which the metal body reacts with the hydrogen toform metal hydride compounds at the surface maintaining the hydrogen atpressures substantially above the dissociation pressure of the formedmetal hydride, intermediate each heating decomposing the surface hydridecompounds. l

3. The method of forming metal hydride compounds from coherent metalbodies which comprises repeatedly heating the metal body in hydrogen toa temperature at which the hydride compound is formed, the pressure ofthe hydrogen being maintained substantially above the equilibriumpressure of the met-al hydride compound at that temperature, eectingintermediate each heating decomposition of the surface metal hydridecompounds by thermal decomposition at higher temperatures at gaspressures be- 1535 lowI the equilibrium pressure at the highertemperature of heating.

4. The method of forming metal hydride compounds from coherent metalbodies which comprises repeatedly heating the metal body in hydrogen toa temperature at which the hydride compound 1s formed, maintaining thepressure of the `hydrogen above the equilibrium pressure of the metalhydride compound formed, eiecting intermediate each heatin adecomposition o fthe surface metal hydride compounds by a reduction infthe hydrogen gas pressures sub` stantially below the dissociationpressure of the metal hydride compound at the tempera# ture to which itis heated.

Y. The'method of: forming uranium' hy dride from coherent uranium metalwhich comprises repeatedly heatinfr the uranium metal in an atmosphereof thydrogen to a tem erature at which uranium hydride may be ormed,maintaining during the heating.

a hydrogen pressure substantially greater than the dissociation pressureof the uranium hydride, intermediate each of the heatings decomposingthe uranium hydride formed.

6. The method of forming uranium hydride from coherent uranium metalwhich comprises repeatedly heatin the uranium metal in an atmosphere ofydrogen to a tem erature at which uranium hydride may be ormed,maintaining during the heating a hydrogen pressure substantially greaterthan the dissociation pressure ofthe uranium hydride, effectingintermediate each of the heatings a thermal decomposition of the uraniumhydride.

7. The method of forming uranium hydride from coherent uran-ium metalwhich comprises repeatedly heatin the uranium metal in an atmosphere ofydrogen to a temperature at which uranium hydride maybe formed,maintaining during the heating a hydrogen pressure substantially greaterthan the dissociation pressure of the uranium hydride, effectingintermediate each of the beatings a decomposition of the uranium hydrideby substantially reducing the hydrogen gas pressure below thedissociation pressure of the metal hydride at the temperature to whichit is heated. u

8. The method of forming uranium hydride from a coherent metal bodywhich comprises alternately heating the metal in a hydrogen atmosphereto temperatures approximating 225o C. and 350o C. maintaining a gaspressure at the lirst mentioned tempera-ture substantially in excess of3.() m. m. mercur and at the last mentioned temperature su stantiallybelow about m. m. mercury pressure.

9. The method of preparing metal `hydride compounds which comprisesenclosing a coherent body of the met-al in 'a container, evacuating thecontainer, degasifying the metal body and container, introducing anatmosphere of hydrogen in the container, heating the metal body to atemperature at which surface formation of metal hydrides is promotedmaintaining at this temperature a pressure of hydrogen in excess of thedissociation pressure of the metal hydride `be ing formed, furtherheating the metal body to more elevated temperatures in gas pressuresubstantially below the dissociation pressure of the metal hydride atthe higher temperature, reducing the `temperature of the metal body tothe lower temperature, and repeating the steps until the entire metalbody has been converted to hydride.

10. The method of preparing uranium metal hydride which comprisesenclosing'aY coherent mass of uranium in a container,

evacuating the container, degasifying the metal and container,introducing. an atmosphere ofhydrogen into the container, and thenrepeatedly heating the metal body to temperatures at which the metalreacts with composition pressure of the uranium hydride` compound atthat temperature and intermediate each of said heating operationseffecting thermal decomposition of the metal hydride formed.

12. The method of preparing uranium metal hydride which comprisesenclosing a coherent mass of uranium in a container, evacuating thecontainer, degasifying the metal and container, introducing anatmosphere of hydrogen into the container, and then repeatedly heatingthe metal body to temperatures at which the metal reacts with thehydrogen atmosphere maintaining a gas pressure substantially in excessto the decomposition pressure of the uranium hydride compound at thattemperature and intermediate each of said heating operations effectingdissociation of the metal hydride formed by heating the hydride compoundunder gas pressure substantially below the equilibrium pressure thereof.

13. The method of preparing uranium metal hydride which comprisesenclosing a 4coherent body of uranium in4 a container, evacuating thecontainer, degasiying the metal body and container, introducing ahydrogen atmosphere in the container, and then repeatedly heating theuranium first at a temperature of about 225 C. in a hydrogen gaspressure materially in excess of about 3.0

m. m. mercury and then to a, temperature of about 350 in a hydrogen gaspressure materially less than about 80 m. m. of mercury until the massof uranium metal has been en- 5 tirely converted to hydrde.

In testimony whereof, I have hereunto subscribed my name this 22nd dayof November, 1929.

FRANK H. DRIGGS.

